Alarms of the type concerned herein are known generally and comprise relatively simple structures. There is a bracket which mounts the motor and may carry electric terminals, switches, etc. mounted thereon. The shaft of the motor protrudes through a support plate and a generally cup-shaped housing or casing is mounted on the support plate co-axially with the shaft. The casing shall be referred to as the stator of the siren. The outer annular flange of the stator has a plurality of perforations intended for cooperation with similar perforations provided on the siren rotor which is mounted on the shaft within the cup-shaped stator. In addition to perforations on the cylindrical wall of the rotor, vanes are provided to promote movement of air through the device thereby creating the turbulence which produces the high-pitched sound desired. One example of such a siren is described in U.S. Pat. No. 3,991,703 owned by the assignee hereof.
Generally, the stator is of cylindrical configuration and provides a cylindrical flange in which the slots or perforations are punched during manufacture. One end of the stator is open so that the stator may be fitted over the rotor. The other end has an annular baffle integral with the flange. Air is intended to be drawn through the stator, channeled by the baffle. The baffle extends radially inward and funnels into the center of the stator when the assembly of stator and rotor is effected. An annular rim is provided which may include an annular recessed portion linking the cylindrical flange to the baffle. The stator may comprise a cylindrical tube carrying the slots and a cup-shaped cap carrying the annular baffle and seated over one end of the tube to complete the assembly of the stator.
Alarms of the type concerned herein are intended to be installed quickly and economically, and are intended to be accessible to the owner or service man during installation, removal, testing, reinstallation and the like which may involve handling of the siren directly. Inadvertent initiation of the operation of the siren while the same is being manipulated may give rise to considerable danger to the fingers of the person handling the device such as the serviceman installing or servicing the alarm. Means for protecting the individual would be considered highly desirable if provided.
One problem with twelve volt devices used on modern automobiles is their current consumption. The desirable end is the improvement of the effectiveness without increasing current drain. Such problem involves operation thereof with the minimization of current usage without loss in effectiveness of the device.
The invention herein involves the discovery that a protective screen or grille can be provided of particular configuration which will enable the operating efficiency of the siren to be improved, provide the required protective function and, unobviously and unexpectedly, improve the harmonics of the sound output to provide emitted sound that is more piercing i.e. higher in sound power output and increased in pitch.